Study On Genetic Evaluation Model And Estimation Of Genetic Parameters Of Lactation Traits In Sanhe Cattle

In this paper,using the test day records of milk yield, fat and protein percentage, fat and protein yield of Sanhe cattle as research materials. Through set the random regression model which fitting the fixed and random effects (additive genetic effects and permanent environmental effects) with different orders of legendre polynomial. Using the evaluation of likelihood ratio and residual variance from diifferent model such as the comprehensive evaluation index to select optimal genetic evaluation model for traits , then the optimal model for each trait were applied to analyze the characters of phenotypic and genetic variation for first 3 lactation. The study obtained:The optimal genetic evaluation model for each trait were: milk yield:LP8-3-5, fat:LP4-4-6, protein:LP3-3-3, fat yield LP3-3-5, protein yield:LP3-4-6.Milk yield: The phenotypic correlations of test days for the first, second and third lactation are -0.128⁰.735,0.057⁰.738,0.164⁰.707, respectively. in the first lactation, genetic correlations between -0.507 and 0.943, of which, the 228th test day has the Highest Heritability up to 0.71, the lowest was 0.184 in early lactation; there was strongly negative genetic correlations for in addition to the third lactation, positive genetic correlation,the heritability were rised in the lactation ; In the third lactation showed strong positive genetic correlation between test days , heritability of test day are medium heritability for all.Fat: there are lower phenotypic correlations during the tset days for three lactation, but there is a strong positive or negative genetic correlation,there are heritability with moderate or above in the first lactation;for the second and third lactation, there are low heritability of test day.Protein: there are lower phenotypic correlations during the test day for lactations, there has strong negative genetic correlation during test days for all lactation,in addition to 305th test day with the rest in the third lactation. The heritability of test day were lower for all lactationsFat yield: The phenotypic correlations of test days for the first lactation is0.617⁰.846,there are weak phtnotypic correlation for the second and third lactation during test days. There are strong Genetic correlation during the day for all lactations, in the first and third lactation there are moderate or above heritability; there has lower genetic heritability for test days of lactations,in addition to 305th test day with the rest in the second lactation (0.252), other heritability of test day are lower (<0.022) .Protein yield: the phenotypic correlations keep positive or negative for all lactations, there are strong positive genetic correlation for all test days in first lactation,except early lactation. there are high heritability For 228^th days of first lactation, and lower for rest.in the second lactation, there are negative phenotypic correlation for79^th,5^th with rest test days, but there are strong positive correlation between 79^th and 5^th test day. There are higher heritability for all test days in second lactation; the later of the third lactation showed high heritability (0.402), the other test day are moderate heritability or below.